1. Field of the Invention
The present invention relates generally to personal audio devices such as headphones that include adaptive noise cancellation (ANC), and, more specifically, to architectural features of an ANC system in which dynamic range of signal pathways is improved by filtering images.
2. Background of the Invention
Wireless telephones, such as mobile/cellular telephones, cordless telephones, and other consumer audio devices, such as MP3 players, are in widespread use. Performance of such devices with respect to intelligibility can be improved by providing adaptive noise canceling (ANC) using a reference microphone to measure ambient acoustic events and then using signal processing to insert an anti-noise signal having an adaptive characteristic into the output of the device to cancel the ambient acoustic events.
The dynamic range of digital audio signal processors, such as the ANC system described above, is set by the width of the signal pathways, which provides a trade-off in circuit complexity, power consumption, and area. Under certain ambient conditions, the dynamic range requirement of an ANC system may be much greater than under nominal conditions, but in order to avoid clipping distortion, the dynamic range of the signal pathways must be sufficient to support the range of signals encountered during operation.
Therefore, it would be desirable to provide a personal audio device, including a wireless telephone that provides noise cancellation that has dynamic range sufficient to avoid clipping distortion, while maintaining low power operation and without requiring significantly larger circuit area.